Wire coating composition



.relation to the amount of solvent .teristicof the .its gelationtemperature, suflices said application is that for portance, as, forexample,

Patented Aug. 24, 1954 WIRE .COATIN G COMPOSITION Emil Olson, 'Muskegon,Mich.,=rassignor.to Ana- 'conflat-Wire and Cable Company, acorporationof Delaware No lDrawing. Application December 29, 1951, Serial No.284,224

3 Claims. 1

This invention relates to an "improved wire coating composition'foruse'in making insulated magnet wire of the :enameled'magnet wire type.

The invention further contemplates the provision of animprovedmagnetwire made by applying toa metallic conductor a-thin film of the newcoating composition. This invention is a .continuation-in-part of myapplication Serial N 0. 76,661, filed February 15, 1949, now Patent No.2,570,476, datedJOctober 9, 1951.

Inmy aforesaid patent, I have described and claimed a wire coatingcomposition that sets by *gelation, consisting essentially of acellulose ester of one or more aliphatic acids containing from 2 to lcarbon atoms, dissolved in a solvent composed essentially of 15 to 30%of a lowermonohydroxy alkanol, 50% to-60% or benzine or one or more ofitsmethyl homologues,-and to 30% of a lowerdialkyl-ketone. esteremployed in this coating composition in is sufficient to impart to thecomposition a viscosity in the range of 600 to 1500 centipoises ata'temperature of 100 F., but in any eventis not less than about 12% byweight of the composition. It is characcomposition-that it sets to anonfiowing solid bygelation upon being cooled to room temperature, say,about 65 F., without solvent evaporation being necessary for suchsolidification to occur.

The aforesaid coating composition hasthe advantage that asingle coatapplied to a wire, in an operation involving drawing the wire through abath of the composition at a temperature above to form on the wire acoating of adequate thickness to meet the dielectric requirements ofWire coating compositions as generally applied to magnet wires; andfurthermore, theprolonged baking operation that is a necessary part ofmaking conventional enameled magnet wires is eliminated. Wires maybecoated with the gelable coating composition at much higher .ratesof.wire travel through the coating bath than is possible with conventionalwire enamels. However, a disadvantage of the coating composition ofmyaforesome purposes its resistance to abrasion is undesirably low. Forthis reason, 'WiI'BS coated with the composition of my aforesaidpatent'have not found many opportunities for use in structures whereabrasion resistance of the Wire coating is of marked imin motor coilswhere thecoils -must be forced into slots in which they fit tightly.

.I have discovered that the abrasion resistance of insulating coatingsformed'on magnet'wire by gelable lacquer coating compositions ofthe'char- -acter described in my aforementioned patentscan be very muchincreased by incorporating in the The amount of .in any .event lacquercomposition 8."!11111011D1'01301fi011 of I a resinous "condensationpolymer of the urea 'formaldehyde or melamine formaldehyde type. Basedon this discovery, therpresent invention. provides a wire coatingcomposition consisting essentially of a solutecomposedessentially 'ofto'95% by weight of a celluloserester"of'atleast one aliphaticacidxcontainingz to "l'carbon'atoms (e. "g.

cellulose acetate butyrate) and 5% 'to. 30% by weight. of a resinouscondensation-polymer with a lower aliphatic aldehyde of a substanceselected from the group consisting of urea, thiourea, cyanamide,guanidinaand melamine'fe. g. urea formaldehyde :resin), said solutebeing dissolved in a solventv composed essentially of approximately 1partby weight of alower monohydroxy alkanol, 3 parts: by Weight "of --asubstance selected from the groupconsisting of benzene and itsmethylhomologues, and 1 part by weight of a lower dialkyl ketone (however,thoroughly satisfactory coating compositions may 'be'madein which theproportions of the-solventconstituents differ substaniially from thosegiven). The proportions of solute to solvent in the coating compositionare suchastto yield a.lacquer which'is fluid'at temperatures above, say,-F., but which gels to a non-flowing solid at-or near room-temperature,say, at about 65 F. For bestresults-the proportion of solute to solventis in the range from -1:.10.to.l:6, i. e. thesolute constitutes from 10%.to 17% .by weight of the'compositionyand the amount of solute usedissuificient to impart to the composition aviscosity at 100 F. in therangefroni-GOO to 1500 centipoises. Generallyit is desirable, but it isnot essential, :to incorporate inthe lacquer-compositionone-ormorechemically-inert pigments or opaquing agents, which ingredients-may beemployed in the proportions of. about 3 to 10 by weight of the solutecomposition. Other ingredients which do not essentially alter the-chaacter of the added as desired.

It is apparent that the coating composition of this invention isgenerally the same as that described in 'my aforementioned Patent 7 No.2,570,476, but with thereplacement of a portion of the celluloseesterwith a corresponding amount of the resinous condensation, polymer..Thesolvent composition is indeed that of. my said-patent, and here, .asin-thatpatent, I use'a l'owermonohydroxy alkanol boiling at atemperature of about 100 C. or less at atmospheric pressure. I may, ofcourse, alsouselowboiling commercial alcohol base. solventssuch .asthe-one composed or'about 92%- .commercial. ethyl alcohol, about-4.8methyl alc0hol,.abo:ut 1.4% methyl-isobutyl ketone, about 1% ethylacetate, .and ab,out.1% hexane mentioned in my.aforementionedpatent. Theparticular solvent material as noted above and as coating compositionalso may be set forth in the claims is, of course, broad enough toinclude such monohydroxy alkanol base s01- vents such as the commercialsolvent as above noted. Similarly, I use a lower dialkyl ketone havingfrom 3 to 6 carbon atoms and boiling at a temperature of about 100 C. orless at atmospheric pressure.

The cellulose esters that are used in the new lacquer composition arethe same that have been used heretofore in dip coating lacquers and inthe wire coating composition of my aforementioned patent, and includecellulose acetate, cellulose propionate, cellulose butyrate, and mixedesters such as cellulose acetate propionate containing, say, to acetyland to 35% propionyl, and cellulose acetate butyrate containing, say,12% to 18% acetyl and 15% to 40% butyryl.

The resinous condensation polymer characteristically employed in thecoating composition of the present invention is a thermosetting resinsuch as is formed by condensation of urea, thiourea, cyanamide,guanidine or melamine with a lower aliphatic aldehyde (usually analdehyde containing from 1 to 4 carbon atoms, and most commonlyformaldehyde), or with such an aldehyde and an alcohol, e. g., butanol.

Such resin may be incorporated in the lacquer composition either in theunpolymerized form or as a partially polymerized product. In eithercase, it is most advantageously incorporated in the form of a solutioncontaining, say 50% to 75% by weight of resin constituents and thebalance solvents such as xylol and butanol. In general, I prefer toemploy the solutions of these condensation polymers which arecommercially avail able. In making up the composition from such asolution, the amount of the non-volatile polymer constituent containedtherein is alone taken into account in determining the soluteproportions of the composition, and the volatile solvent constituents ofthe polymer solution are taken into acount as components of the solventof the lacquer composition.

Although particularly satisfactory results are obtained by employing aurea formaldehyde condensation polymer or other condensation polymer ofthe character mentioned above in preparing lacquer compositionsaccording to the invention, any thermosetting resin which is compatiblewith the cellulose ester and which can be dissolved in the solventcomponent of the composition may be employed with beneficial results.

Following is an example of a typical Wire coating composition preparedin accordance with this invention:

In this composition, the solids constitute 14.2 parts by weight, or13.5% by weight of the composition, and the solvent componentsconstitute 90 parts by weight, or 86.5% by weight of the composition.This composition has a viscosity of about 1000 to 1200 centipoises at100 F. and

guanidine, and melamine solidifies by gelation when cooled to atemperature of about 65 F.

Coating compositions prepared in accordance with the invention are mostadvantageously applied to wires by the method described and claimed inUnited States Patent No. 2,547,047 to Harry L. Saums, John H. Vail andHoward W. Sturgis, using apparatus of the character described andclaimed in United States Patent No. 2,558,993 to Howard W. Sturgis andEmil I-I. Olson. Briefly, the method of applying the coating compositionto the wire involves passing the wire into a bath of the compositionmaintained at a temperature well above its gelation temperature, andthen withdrawing the wire with a film of the coating compositionadhering thereto. This film cools almost at once as the wire emergesinto the room atmosphere to below its gelation temperature and therebysets almost immediately to a non-flowing solid film. Eventually thevolatile constituents of the gelled film evaporate, leaving a. wirecoated with an intimate blend of the non-volatile constituents of thelacquer. The finished wire thus comprises a metallic conductor havingthereon a thin substantially uniform and continuous coating composedessentially of 70% to 95% by weight of a cellulose ester of at least onealiphatic acid containing from 2 to 4 carbon atoms (e. g., celluloseacetate butyrate), intimately blended with 5% to 30% by weight of aresinous condensation polymer of a lower aliphatic aldehyde with asubstance selected from the group consisting of urea, thiourea,cyanamide,

(e. g., a urea formaldehyde resin).

It is a major advantage of coating compositions prepared in accordancewith the invention that the insulating film formed by its use on thesurface of the wire is substantially continuous with but very few andwidely separated pinholes even when the coating is applied at a highrate of wire travel. Also, the coating is uniform in thickness about theperiphery of the wire and along its length, and, most important. it istightly adherent to the wire and highly resistant to abrasion.

The remarkably improved characteristics of wire coated with thecomposition of this invention, in comparison with a wire coated with agelable lacquer prepared in accordance with my aforementioned patent, isillustrated by the test results summarized in Table I below. In each ofthe tests mentioned, the wire designated as wire A was prepared inaccordance with this invention by coating a bare No. 36 A. W. G. copperconductor with the particular coating composition given by way ofexample above; and the wire designated as wire B was made by applying toa bare No. 36' A. W. G. copper conductor a coating composition identicalin all respects with that of the above example, save only that the ureaformaldehyde was omitted and a corresponding increase was made in theamount of cellulose acetate butyrate employed in the composition.

Table I Wire A Wire B Scrape Test (wire a ed 1 week Continuity Test u 23 3 Abrasion Test (wire aged 1 day) i l, 850 40 The manner in which thetests reported in the table were carried out is as follows:

Scrape test.-The so-called Delco scrape test was used in obtaining thedata given in the table. In this test the wire is pulled horizontallyunder the point of a needle, the needle being mounted so that it bearson the wire with a weight that can be varied. The needle and the wireare connected together in a low-voltage electrical circuit. The weight(in ounces) on the needle which is just suificient to cause the needleto scrape through the coating on the wire and complete the electricalcircuit is taken as an index of the scrape resistance of the wire. Thegreater the weight with which the needle must be loaded, the better isthe quality of the coating insofar as regards its scrape resistance.

Continuity test-To determine the continuity of a coating film on a wire,the coated wire is drawn through a pool of mercury. The wire and mercuryare connected together in an electric circuit which is completedwhenever the mercury comes in direct contact with the metal of the wirethrough a perforation in the coating. The number of times the circuit isthus completed 4 per hundred feet of wire drawn through the mercury poolis taken as an index of The smaller the number of such circuitcompletions, the better is the quality of the wire.

Abrasion test-The abrasion resistance of the coating compositions asgiven in the above table was determined by the use of an apparatuscomprising twelve spokes, each one-quarter inch in diameter and arrangedin the form of a cylindrical cage, mounted for rotation about ahorizontal axis. The wire to be tested is anchored at one end, and theother end is passed over the spokes, being held down against the spokesby a weight attached to its other end. The metallic conductor of thewire and the spokes of the cage are connect-ed together in an electricalcircuit and the cage is rotated so that each spoke rubs film continuity.

along the coating on the wire with each revolution of the cage. When thespokes have worn through the coating and make contact with the metallicconductor, an electrical circuit which stops the apparatus is completed.Thenumber of revolutions which the cage makes until such circuit iscompleted is an index of the resistance of the wire to abrasion. Thegreater the number of rotations which the cage makes before the circuitis completed, the greater is the abrasion resistance of the coating.

It will be noted from Table I above that wire A, made in accordance withthe present invention, was greatly superior in scrape resistance and in6 the new wire showed marked improvement over the wire made by themethod of my aforementioned patent. These outstanding test results areindicative of the much wider range of usefulness under conditionsimposing substantial abuse on he insulating coating, of wire made inaccordance with this invention.

I claim:

1. A wire coating composition consisting essentially of a solutecomposed essentially of 70% to 95% by weight of cellulose acetatebutyrate and 5% to 30% by weight of a urea formaldehyde resinouscondensation product dissolved in a solvent composed essentially ofapproximately 1 part by weight of a lower monohydrcxy alkanol containing1-5 carbon atoms and having a boiling point of about 100 C., 3 parts byweight of a substance selected from the group consisting of benzene andits methyl homologues, and 1 part by weight of a lower dialkyl ketonecontaining 3-6 carbon atoms and having a boiling point of about 100 C.,said composition having a viscosity in the range from 600 to 1500centipoises at 100 F. and gelling to a non-flowing solid at about 2. Awire coating composition consisting essentially of a solute 95% byweight of a cellulose est-er of at least one allphatic acid containingfrom 2 to 4 carbon atoms and 5% to 30% by weight of a resinouscondensation polymer of a lower aliphatic aldehyde with a substanceselected from the group consisting of urea, thiourea, cyanamide,guanidine, and melamine, said solute being dissolved in a solventcomposed essentially of approximately 1 part by weight of a lowermonohydroxy alkanol containing 1-5 carbon atoms and having a boilingpoint of about 100 C., 3 parts by weight of a substance selected fromthe group consisting of benzene and its methyl homologues, and 1 part byweight of a lower dialkyl ketone containing 3-6 carbon atoms and havinga boiling point of about 100 C., said composition having a viscosity inthe range from 600 to 1500 centipoises at 100 F. and gelling to anon-flowing solid at about F.

3. Magnet wire comprising a metallic conductor having thereon a thinsubstantially uniform and continuous coating composed of approximatelyto by weight of cellulose acetate butyrate intimately blended with 5% to30% by weight of a urea formaldehyde resinous condensation polymer.

References Cited in the file of this patent UNITED STATES PATENTS Numbercomposed essentially of 70% to

2. A WIRE COATING COMPOSITION CONSISTING ESSENTIALLY OF A SOLUTECOMPOSED ESSENTIALLY OF 70% TO 95% BY WEIGHT OF A CELLULOSE ESTER OF ATLEAST ONE ALIPHATIC ACID CONTAINING FROM 2 TO 4 CARBON ATOMS AND 5% TO30% BY WEIGHT OF A RESINOUS CONDENSATION POLYMER OF A LOWER ALIPHATICALDEHYDE WITH A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF UREA,THIOUREA, CYANAMIDE, GUANIDINE, AND MELAMINE, SAID SOLUTE BEINGDISSOLVED IN A SOLVENT COMPOSED ESSENTIALLY OF APPROXIMATELY 1 PART BYWEIGHT OF A LOWER MONOHYDROXY ALKANOL CONTAINING 1-5 CARBON ATOMS ANDHAVING A BOILING POINT OF ABOUT 100* C., 3 PARTS BY WEIGHT OF ASUBSTANCE SELECTED FROM THE GROUP CONSISTING OF BENZENE AND ITS METHYLHOMOLOGUES, AND 1 PART BY WEIGHT OF A LOWER DIALKYL KETONE CONTAINING3-6 CARBON ATOMS AND HAVING A BOILING POINT OF ABOUT 100*., SAIDCOMPOSITION HAVING A VISCOSITY IN THE RANGE FROM 600 TO 1500 CENTIPOISESAT 100* F. AND GELLING TO A NON-FLOWING SOLID AT ABOUT 65* F.